1. Field of the Invention
This invention relates to releasable backstopping clutches and, more particularly, to a backstopping clutch assembly having a safety mechanism to prevent uncontrolled release of the clutch.
2. Disclosure of Related Art
In many motor driven systems, it is desirable to prevent or limit movement of system components in one direction. For example, mining operations typically use inclined conveyors to convey material to a surface location or other outlet. It is desirable to prevent or limit reverse movement of the conveyor in the event of a loss of power or a failure of a driveline component such as the motor or motors, gearboxes or couplings in order to prevent material from moving backwards on the conveyor and causing damage to the system and significant injuries to personnel operating the system.
Backstopping clutches are typically used to prevent reverse rotation of rotating system components. A backstopping clutch includes an inner member that is mounted to a shaft driven by one or more motors for rotation with the shaft about a rotational axis. An outer member is disposed radially outward of the inner member and is generally fixed against rotation through coupling with a fixed support structure such as a torque arm or gear box (which itself may be coupled to surrounding, fixed structures). A plurality of torque transmission members (e.g., rollers, sprags, etc.) are disposed radially between the inner and outer members. The torque transmission members and/or inner or outer members are shaped such that when the motor drives the shaft and inner member in one rotational direction, the torque transmission members assume a first position permitting relative rotation of the inner and outer members (i.e., permitting the inner member to freewheel). When the driven shaft and inner member are driven in the opposite rotational direction (e.g. by the force of the load of the material on a conveyor upon failure of a motor), the torque transmission members assume a second position and forcefully engage the inner and outer members and prevent the inner member and driven shaft from rotating relative to the fixed outer member.
Some backstopping clutches are releasable to enable easier servicing of the clutch and surrounding motor driven structures and to limit torque on the clutch and structures. In a releasable backstopping clutch, the support structure is releasably coupled to the outer member of the clutch. When the support structure is uncoupled from the outer member, the engaged outer and inner members of the clutch are permitted to rotate in the direction opposite the freewheeling direction.
Releasable backstopping clutches have not obtained widespread acceptance because releasing the clutch creates significant safety issues. In particular, if the clutch is released for a long enough period of time, the accumulated kinetic energy of the load may exceed the ability of the release mechanism to reengage and prevent further movement.
The inventors herein have recognized a need for a releasable backstopping clutch assembly that will minimize and/or eliminate one or more of the above-identified deficiencies.